As shown in FIG. 9, in a MIMO scheme, downlink signals Stx1 to StxN to the terminal side are transmitted from N (N=4 in this example) base station-side antennas (hereinafter, referred to as transmitting antennas) Atx1 to AtxN, and are received in M (M=2 in this example) terminal-side antennas (hereinafter, referred to as receiving antennas) Arx1 to ArxM.
Therefore, N×M propagation channels (channels) are assumed between each transmitting antenna and each receiving antenna, and U (for example, U=4) paths different from each other for each channel are assumed. In a case where the propagation characteristics of each channel inclusive of a path are set to H (1, 1, 1 to U) to H (N, M, 1 to U), and a mobile terminal supporting the MIMO scheme, a circuit used in the mobile terminal, or the like is tested, it is necessary to perform an arithmetic operation process in which the effects of propagation characteristics of each channel and the characteristics of a loss, a delay, a Doppler shift or the like for a path are taken into account with respect to a downlink signal, to finally generate received signals Srx1 to SrxM which are output from M receiving antennas Arx1 to ArxM, and to give the generated signals to a test object 1.
On the other hand, in recent years, as a modulation scheme, high-speed signal transmission based on a multicarrier modulation scheme such as orthogonal frequency division multiplexing (OFDM), universal filtered multicarrier (UFMC), generalized frequency division multiplexing (GFDM), or filtered bank multi-carrier (FBMC) is realized, and a MIMO scheme system capable of higher-speed information communication is realized by a combination of this multicarrier modulation scheme and the MIMO scheme, whereby a device for testing the system is required.
In addition, in the next-generation (fifth generation) communication scheme, it is proposed to use a higher frequency band. In a case where a frequency band used in communication in this manner becomes higher, the size of each antenna can be formed to be small. Therefore, so-called beam forming becomes possible in which an array antenna structure having a large number of antenna elements arranged lengthwise and breadthwise is adopted, and radio waves are efficiently radiated in a direction in which a mobile terminal of a communication object is present, by phase control of a downlink signal given to these antenna elements. Therefore, in a testing device in which such a next-generation mobile terminal is a test object, an arithmetic operation process of beam forming for a large number of antennas arrayed is required.
FIG. 10 shows a configuration example of a testing device for testing a system in which a multicarrier modulation scheme, a MIMO scheme and a beam forming process based on an array antenna are combined.
This testing device 10 is a device supporting OFDM for performing communication with a terminal using K subcarriers as one of the multicarrier modulation schemes, and a layer frequency domain signal generation unit 11 generates and outputs modulation signals (constellation data) Ssym(1, 1) to Ssym(1, K), Ssym(2, 1) to Ssym(2, K), . . . , Ssym(R, 1) to Ssym(R, K) for each of K subcarriers with respect to R series of transmission data (called layer or stream) to be transmitted to a test object. This modulation signal Ssym is a signal in a frequency domain including R series of data having K constellation data lined up on a frequency axis, for each OFDM symbol.
These modulation signals Ssym are input to a beam forming processing unit 12, are arithmetically processed so that the beam characteristics of radio waves emitted from N transmitting antennas are set to desired characteristics, and are converted into beam forming process signals Sbf(1, 1) to Sbf(1, K), Sbf(2, 1) to Sbf(2, K), . . . , Sbf(N, 1) to Sbf(N, K) for each of K subcarriers per transmitting antenna. Meanwhile, in the following description inclusive of the drawing, a set of j signals Sx(i, 1) to Sx(i, j) may be abbreviated to Sx(i, 1 to j).
These beam forming process signals Sbf are input to N sets of time domain signal generation units 13(1) to 13(N). Each time domain signal generation unit 13(i) (i=1 to N) performs an inverse Fourier transform (IFFT) process, a cyclic prefix (CP) addition process, a band-limiting process, or the like with respect to a set of K beam forming process signals Sbf (i, 1 to K), and converts the signals into signals on a time axis specified in an OFDM scheme.
Thereby, transmission signals (downlink signals) Stx1 to StxN given to N transmitting antennas Atx1 to AtxN are output from the respective time domain signal generation units 13(1) to 13(N).
These transmission signals Stx1 to StxN are input to a propagation channel simulator 20 that simulates the characteristics of the propagation channel of N×M channels.
The propagation channel simulator 20 takes N×M channels formed between N transmitting antennas and M receiving antennas and U paths for each of the channels into consideration, adds a desired delay and fading to these N×M×U paths, and virtually generates signals received by the M receiving antennas.
This propagation channel simulator 20 is used in giving Rayleigh fading indicating the distribution of reception level fluctuations in wireless communication, and includes a delay setting unit 21 that gives a predetermined delay to U paths which are set in N series of transmission signals Stx1 to StxN to be output, a fading setting unit 22 that obtains the characteristics of a propagation channel of Rayleigh distribution to which a Doppler shift and MIMO-correlated information are given, and an arithmetic operation unit 23 that generates signals Srx1 to SrxM received in the M receiving antennas through N×M×U virtual propagation channels by a product-sum arithmetic operation (matrix multiplication) using all paths' delay processing signals Stx (1, 1, 1 to U), Stx (2, 1, 1 to U), . . . , Stx (N, M, 1 to U) which are output from the delay setting unit 21 and propagation characteristics H (1, 1, 1 to U), H (2, 1, 1 to U), . . . , H (N, M, 1 to U) obtained by the fading setting unit 22.
Here, the delay setting unit 21 gives a desired delay to each path by, for example, a combination of a delay of one sample unit based on a memory and a delay of one sample or less based on a resampling filter.
In addition, the arithmetic operation process of the arithmetic operation unit 23 is, for example, as follows.Srx1=ΣH(1,1,i)·Stx(1,1,i)+ΣH(2,1,i)·Stx(2,1,i)+ . . .+ΣH(N,1,i)·Stx(N,1,i)Srx2=ΣH(1,2,i)·Stx(1,2,i)+ΣH(2,2,i)·Stx(2,2,i)+ . . .+ΣH(N,2,i)·Stx(N,2,i) . . .SrxM=ΣH(1,M,i)·Stx(1,M,i)+ΣH(2,M,i)·Stx(2,M,i)+ . . .+ΣH(N,M,i)·Stx(N,M,i)
Here, the symbol Σ indicates the sum of i=1 to U.
The received signals Srx1 to SrxM obtained in this manner are given to the test object 1, and thus it is possible to test the operation of the test object 1 for a propagation channel between the transmitting and receiving antennas which is set on the testing device side.
Meanwhile, a device for testing a system in which a propagation channel simulator is not included, but the multicarrier modulation scheme and the MIMO scheme are combined as described above is disclosed in, for example, the following Patent Document 1.